Many multi-component compositions that are solid are made by extrusion. For example, the majority of soap and detergent bars consumed worldwide are produced by extrusion. Extrusion requires a thermoplastic mass that can tolerate extensive shear. However, an alternative process is required to produce compositions whose structure, geometric properties and constituents are shear sensitive. The most commonly employed method for shaping shear sensitive solids is casting.
Casting involves transfer of the composition in the molten state into some form of mold and the subsequent solidification of this mixture by quiescent cooling, i.e., cooling without mixing. The transfer can be by simple pouring under gravity or by injection under pressure. The molten mixture can range from a simple Newtonion liquid to a viscoelastic paste.
One problem that occurs when using individual molds that are filled substantially to capacity (so called “capacity molds”) for casting thermal setting compositions is the development of imperfections due to shrinkage during cooling. When the mold is made of relatively easily deformable materials such as plastic film, the most common imperfections produced by thermal shrinkage are dents, wrinkles, and air cavities within the interior of the product. This is a particular problem when the mold also serves as all or a part of the packaging for such compositions at the point of sale where appearance is a key indicator of product quality.
In contrast, when the mold is made of rigid walls, holes or occlusion can occur within the mass that are often only evident in use or if the solid is cut. The problems caused by thermal shrinkage are particularly severe when the temperature of the molten composition is high, or when the composition includes multiple phases that have a high coefficient of thermal expansion, e.g., a composition such as an aerated bar that contains a dispersed gas. Aeration exacerbates the shrinkage of all formulations and causes the development of pronounced defects that are easily seen by the consumer.
One approach that has been suggested to overcome the problem of shrinkage of thermal setting soap or detergent compositions during cooling involves transferring the molten mass into an essentially elastic polymer casing which can accommodate the shrinkage. However, since such casings are less than 100 microns in thickness, either only very simple shapes are possible or an external shaping device or mold is required for more sophisticated shapes. Furthermore, because of its elastic nature and thinness, such “sausage casing” films are not very robust and additional packaging is usually required.
A similar problem of defects produced by thermal shrinkage is also frequently encountered in the molding of plastics, e.g., molding of thermosets into capacity molds. Three main approaches have been employed in the polymer industry to overcome these problems: reduction in the coefficient of thermal expansion via formulation; development of very complex molds that can adjust volume or pressure in response to thermal shrinkage; and inclusion of a gas “buffer” at the mold wall that takes up the shrinkage. All of these approaches, however, require complex molds and are not suitable for application when the mold also serves as part or all of the packaging for the composition at the point of sales.
The following publications form a part of the related art:
U.S. Patent Publication 2005/0014665 to Nadakatti et al published Jan. 20, 2005 describes a continuous process for casting employing a continuous tube of flexible material. The tube acts as a sleeve. The composition is shaped in or on a suitable mold.
EP 0321179 to Instone et al published Jun. 21, 1989 describes a method of casting soap into a pack made out of flexible film. The pack has the form of a bag or sachet. Other shapes required a shaping means such as platens.
WO98/51773 to Nadakatti et al published Nov. 19, 1998 describes a split cavity casting mold including at least two rigid complimentary dies which upon engagement defines a cavity corresponding to a desired shape of the cast article.
U.S. Pat. No. 3,149,188 to Schmitt issued on Sep. 15, 1964 describes a method of manufacturing a ready-to-use cake of transparent soap. The method includes the steps of casting a liquid mass into transparent plastic mold, permitting the liquid mass to cool and maintaining the composition in the sealed mold until ready to use.
Fr 910,256 to Lonchambon published Nov. 10, 1944 describes a method of casting liquid soap into a preformed mold that is retained as an envelope around the soap and thus delivered to the consumer.
EP 0854092 to Tabaroni et al published Jul. 22, 1998 describes a container made from a thermoformable and heat sealable material including a pair of thermoformed halves heat sealed along an edge so as to create a stiffening rib. The halves are obtained by folding a single sheet folded along its lower edge.
WO 94/08852 to Tabaroni et al describes a container made of a thermoformable and heat sealable material, its method of manufacture and an apparatus for carrying out this method.
U.S. Pat. No. 5,669,208 to Tabaroni et al issued Sep. 23, 1997 describes a container formed in a thermoformable and heat weldable material including an inlet having an inlet wall portions which are elastic so that the inlet is self closing prior to permanent sealing. A system including blow molding and filling stations is also described.
JP 10-291230 to Kazuharu published Nov. 4, 1998 describes a method for injection molding of resins utilizing gas to prevent surface defects.
JP 10-323340 to Yoshimitsu published Dec. 12, 1997 discloses a mold for injection molding of plastic that is linked to a hydraulic cylinder which serves to pressurize the contents of the mold thereby eliminating defects caused by shrinkage during cooling.
JP 08-099163 to Mitsuhiro et al published Apr. 16, 1994 describes a method and mold for casting metal that includes pressurized pins to adjust volume within the mold during cooling and solidification.
U.S. Pat. No. 5,615,731 to Roehrig et al issued on Apr. 1, 1997 describes a ridged mold for casting parts having an I-shaped cross-section. The mold includes flange or bulges shaped in a particular way that forces shrinkage in a preferred direction.
U.S. Pat. No. 5,882,557 to Kazuhiro et al issued Mar. 16, 1999 described a mold with members made of a silicone rubber for fabricating an ultrasonic coupler made from an aqueous solution of polyvinyl alcohol.
U.S. Pat. No. 5,255,729 to Cook et al issued Oct. 26, 1993 describes a process for forming net shaped parts which includes the step of heating the mold and contents such that their coefficients of thermal expansion are matched thereby eliminating shrinkage.
EP 0273769 to Stone et al published Jul. 6, 1988 describes an injection molding apparatus that employs a hydraulic system to pressure mold and compensate for shrinkage during cooling.
U.S. Pat. No. 4,364,878 to Laliberto describes a mold for fabricating lenses that has movable mold inserts (“walls”) that are used to compensate for shrinkage.
The present invention seeks improvements over deficiencies in the known art. Among the one or more problems addressed include the development of a capacity mold for thermal setting compositions that eliminates stress induced defects from thermal shrinkage of the composition during cooling.